Copolyamides and compositions based on same

ABSTRACT

The invention concerns copolyamides obtained by using multifunctional monomers. It consists in using at least one multifunctional monomer comprising at least three reactive functions and at least another multifunctional monomer, in amounts such that the terminal group concentrations are balanced. The copolyamides are more particularly high viscosity copolyamides. The invention also concerns compositions based on said copolyamides.

The present invention relates to copolyamides obtained usingmultifunctional monomers. The invention relates more particularly tohigh-viscosity polyamides. The invention also relates to compositionsbased on these copolyamides.

Formed thermoplastic polyamides are used for many applications. Examplesthat may be mentioned include yarns, fibers and filaments, films andarticles obtained by molding, injection-molding or extrusion. Forcertain applications, or for certain forming processes, it isoccasionally preferred to use polyamides with a high melt viscosity.This is the case, for example, for the polyamide fibers used for themanufacture of paper machine felts. This is also the case, for example,for processes for forming articles by extrusion blow-molding. During theimplementation of the latter process, it is generally important for theextruded component not to deform, or to deform only very little underits own weight. The mechanical properties of the material, such as theelastic modulus and the impact strength, must moreover not be affected,or only very little affected.

Several solutions are known for obtaining high-viscosity polyamides. Afirst solution consists in performing a solid-phase postcondensation onlinear polyamides. The postcondensation times are long, which gives riseto high production costs.

Another solution is described in patent application WO 99/03909. Itdescribes copolyamides obtained using a multifunctional monomercomprising a reactive function that forms amide bonds, chosen from acidsand amines, and at least two reactive functions that form amide bonds,which are of different nature and complementary to the previousfunction. These copolyamides have, for an identicalmelt-poly-condensation time, a higher melt viscosity than that of linearpolyamides.

However, the copolyamides described in the document have a viscositythat it is sought further to improve. Another object is to achieveequivalent viscosities with shorter and/or controlled polymerizationcycle times.

Within the technical field of copolyamides obtained from monomersincluding at least one multi-functional monomer the known documentsinclude WO 00/35992. This document describes copolyamides obtainedstarting from a mixture of monomers including the following: a monomerAB, a monomer A_(v) where v≧3, a monomer B_(w) where w≧2, A and B beingacid or amine functions, such that they are capable of forming amideunits between them. The document teaches that it is not possible toobtain gel-free polymers unless the number of functions of the monomersand the amount of each monomer used are selected so as to satisfy amathematical relation, defining a fairly restricted range ofproportions. It is said that, outside of the range, gels are formed.Without going into the details of the formula, the document may beconsidered to teach that the monomers A_(v) and B_(w), and theirproportions, must be selected so as to cause strong disequilibration ofthe amounts of functions of the two types provided by the monomers. Thisdocument does not describe the properties of the materials obtained, andso it is difficult to evaluate its import from a single reading.

The object of the present invention is to propose novel copolyamides,free of gel, and more particularly copolyamides obtained starting frommultifunctional monomers which are present such that the amounts offunctions of each type are substantially equilibrated. The novelcopolyamides have a higher melt viscosity than that of the polyamidesdescribed in document WO 99/03909 or, for an equivalent viscosity, maybe obtained with shorter polymerization cycles.

To this end, the invention proposes a copolyamide, comprisingmacromolecular units derived from at least the following monomers:

-   -   (I) at least one difunctional monomer represented by the        abbreviation AB    -   (II) at least one multifunctional monomer represented by the        abbreviation A_(a) in which A represents a function of the        carboxylic acid type    -   (III) at least one multifunctional monomer represented by the        abbreviation B_(b) in which B represents a function of the amine        type    -   the functions A and B being capable of reacting with each other        to form an amide unit,    -   a and b being numbers that satisfy the following relationships:        -   a≧2        -   b≧2        -   a≧3 if b=2        -   b≧3 if a=2    -   the ratio $\frac{ax}{{ax} + {by}}$    -    is between 0.4 and 0.6,    -   in which x represents the number of moles of monomer (II) and y        represents the number of moles of monomer (III)    -   the ratio        $\frac{{ax} + {by}}{\left( {a + b} \right)*\left( {x + y + {0.9z}} \right)}$    -    being less than 0.12%    -   in which z represents the number of moles of monomer (I).

The term “multifunctional monomer” means a monomer comprising at leasttwo reactive functions.

In the present patent application, the abbreviations (AB, A_(a), B_(b))are used to denote organic or organometallic molecules serving asmonomers. The monomers are molecules with reactive functions of acidtype A or of amine type B, capable together of forming amide bonds.

The acid-type functions are advantageously chosen from carboxylic acid,acid halide and ester functions. The amine-type functions areadvantageously chosen from amines, preferably primary amines, and aminesalts.

The number of functions of each type is represented for the variousmonomers by the letters a, b. The monomers (I) comprise a function ofeach type.

The monomers (II) and (III) comprise at least 2 functions, andpreferably not more than 10. The number of functions for each (a and b,respectively) is preferably chosen from 3, 4, 5 and 6. Moreover, if oneof the monomers (II) or (III) contains two functions, the other containsat least three of them.

The number of moles of monomer (II) from which the copolyamide isobtained is denoted by the letter x. The number of moles of monomer(III) from which the copolyamide is obtained is denoted by the letter y.The number of moles of monomer (I) from which the copolyamide isobtained is denoted by the letter z.

The ratio α, $\alpha = \frac{a\quad x}{{a\quad x} + {by}}$is between 0.4 and 0.6 and preferably between 0.45 and 0.55. Even morepreferably, it is substantially equal to 0.5. This condition isequivalent to writing that the number of amine-type functions and thenumber of acid-type functions in the monomers (II) and (III) used toobtain the polymer is relatively, or even substantially totally,equilibrated.

According to one characteristic of the invention, the ratio β,$\beta = \frac{{a\quad x} + {by}}{\left( {a + b} \right)*\left( {x + y + {0.9*z}} \right)}$is less than 0.12% and preferably less than or equal to 0.1%. The use ofmonomers (II) and (III) in larger amounts may lead to crosslinkedcopolymers. As a guide, and with no limitation to the invention, thefactor 0.9 applied to the number of moles z of the monomer of type ABtakes into account that the monomers (I) generally do not reactentirely. The above ratio is thus close to a ratio between the number ofmoles of monomers (II) and (III) and the number of moles of repeatingunits in the polyamide.

According to another characteristic of the invention, the ratio χ,$\chi = \frac{x + y}{x + y + {0.9*z}}$is preferably less than 0.2%.

The monomers (II) and the monomers (III) may consist, respectively, of amixture of several monomers A_(ai) and B_(bj) in which a_(i) and b_(j)satisfy the conditions defined above for a, b, with the possibleexception of the calculation of the ratios α, β and χ, for which thefollowing apply:${- {ax}} = {\sum\limits_{i}^{\quad}\quad{a_{i}\quad x_{i}}}$for the calculation of α and β${- {by}} = {\sum\limits_{i}^{\quad}\quad{b_{j}\quad y_{j}}}$for the calculation of α and β${- x} = {\sum\limits_{i}^{\quad}\quad x_{i}}$for the calculation of β and χ${- y} = {\sum\limits_{j}^{\quad}\quad y_{j}}$for the calculation of β and χ in which

-   -   a_(i) represents the number of acid-type functions in a        monomer (II) referenced i    -   b_(j) represents the number of acid-type functions in a        monomer (III) referenced j    -   x_(i) represents the number of moles of a monomer (II)        referenced i    -   y_(j) represents the number of moles of a monomer (III)        referenced j.

The monomers (I) are advantageously chosen from:

-   -   ε-caprolactam and/or the corresponding amino acid: aminocaproic        acid, and/or    -   para- or meta-aminobenzoic acid, and/or    -   11-aminoundecanoic acid, and/or    -   lauryllactam and/or the corresponding amino acid:        12-aminododecanoic acid.

More generally, the monomers (I) may be the monomers used to manufacturelinear thermoplastic polyamides. Thus, mention may be made ofω-amino-alkanoic compounds comprising a hydrocarbon-based chaincontaining from 4 to 12 carbon atoms, or the lactams derived from theseamino acids, for instance ε-caprolactam. Mixtures of monomerscorresponding to the abbreviation AB, preferably chosen from themonomers proposed above, may also be used.

The monomers (II) and (III) are multifunctional monomers all of whosereactive functions are identical. The reactive functions of the monomer(II) are different from the reactive functions of the monomer (III), butboth are capable of forming amide units between them. Themultifunctional monomers all of whose functions are identical are oftencalled “core monomers”.

A first category of compounds which are suitable as monomers (II) and/or(III) consists of molecules or macromolecules with an arborescent ordendritic structure. Examples that may be mentioned include polyaminescomprising a high number of amine units. Mention may also be made of thetotally aromatic dendrimers described in patent applications WO95/06081.

A second category of compounds which are suitable as monomers (II)and/or (III) consists of compounds that may be chosen from the compoundsmentioned below.

Mention is made of multifunctional compounds chosen from the compoundsof formula (a)

in which

-   -   C is a covalent bond or an aliphatic hydrocarbon-based radical        that may comprise hetero atoms, and containing from 1 to 20        carbon atoms and preferably from 1 to 6 carbon atoms,    -   X is a radical        if it is a monomer (III),        or a radical        if it is a monomer (II)    -   R₄ is a linear or cyclic, aromatic or aliphatic        hydrocarbon-based radical containing at least two carbon atoms        and possibly comprising hetero atoms,    -   m is an integer between 3 and 8 (limits included).

According to one preferred embodiment of the invention the monomers (II)and (III) each contain at least three reactive functions. In this casethe monomers (II) and (III) are advantageously selected from themonomers represented by the formula (a) shown above, X representing forthe monomers (III) and (II) respectively a radical

According to yet another preferred characteristic, the radical R₄ iseither a cycloaliphatic radical such as the tetravalent cyclohexanoylradical, or a 1,1,1-triylpropane or 1,2,3-triylpropane radical.

Examples of other radicals R₄ suitable for the invention that may bementioned include substituted or unsubstituted trivalent phenyl andcyclohexanyl radicals, tetravalent diaminopolymethylene radicals with anumber of methylene groups advantageously between 2 and 12, such as theradical derived from EDTA (ethylenediaminotetraacetic acid), octavalentcyclohexanoyl or cyclohexadinonyl radicals, and radicals derived fromcompounds obtained from the reaction of polyols such as glycol,pentaerythritol, sorbitol or mannitol with acrylonitrile.

Radical A is preferably a methylene or polymethylene radical such as anethyl, propyl or butyl radical, or a polyoxyalkylene radical such as apolyoxyethylene radical.

According to one preferred embodiment of the invention, the number m isgreater than or equal to 3 and advantageously equal to 3 or 4.

The reactive function of the multifunctional compound represented by thesymbol X—H is a function capable of forming an amide function.

Examples of multifunctional compounds of formula (a) that may bementioned include 2,2,6,6-tetrakis(β-carboxyethyl)cyclohexanone,diaminopropane-N,N,N′N′-tetraacetic acid of the following formula:

or compounds derived from the reaction of trimethylolpropane or glycerolwith propylene oxide and amination of the hydroxide end groups; thelatter compounds are sold under the trade name Jeffamines T® by thecompany Huntsman, and have the general formula:

in which:

-   -   R₄ represents a 1,1,1-triylpropane or 1,2,3-tri-ylpropane        radical,    -   A represents a polyoxyethylene radical.

Examples of multifunctional compounds that may be suitable areespecially mentioned in document U.S. Pat. No. 5,346,984, in documentU.S. Pat. No. 5,959,069, in document WO 96/35739 and in document EP 672703.

The following may be mentioned more particularly:

-   nitrilotrialkylamines, in particular nitrilotriethyl-amine,    dialkylenetriamines, in particular diethylene-triamine,    trialkylenetetramines and tetraalkylene-pentamines, the alkylene    preferably being ethylene, 4-aminoethyl-1,8-octanediamine.

Mention is also made of the dendrimers of formula (II)

-   (R₂—N— (CH₂)_(n))₂—N—(CH₂)_(x)—N—((CH₂)_(n)—NR₂)₂ (II)    in which-   R is a hydrogen atom or a group —(CH₂)_(n)—NR¹ ₂ in which-   R¹ is a hydrogen atom or a group —(CH₂)_(n)—NR² ₂ in which-   R² is a hydrogen atom or a group —(CH₂)_(n)—NR³ ₂ in which-   R³ is a hydrogen atom or a group —(CH₂)_(n)—NH₂,-   n being an integer between 2 and 6,-   x being an integer between 2 and 14,-   n is preferably an integer between 3 and 4, in particular 3, and x    is preferably an integer between 2 and 6, preferably between 2 and 4    (limits included), in particular 2. Each radical R may be chosen    independently of the others. The radical R is preferably a hydrogen    atom or a group —(CH₂)_(n)—NH2.

Mention is also made of multifunctional compounds containing 3 to 10carboxylic acid groups, preferably 3 or 4. Among these, the ones thatare preferred are the compounds containing an aromatic and/orheterocyclic ring, for example benzyl, naphthyl, anthracenyl, biphenyland triphenyl radicals, or heterocycles, for instance pyridine,bipyridine, pyrrole, indole, furan, thiophene, purine, quinoline,phenanthrene, porphyrin, phthalocyanine and naphthalo-cyanine.3,5,3′,5′-Biphenyltetracarboxylic acid, acids derived fromphthalocyanine and from naphthalocyanine,3,5,3′,5′-biphenyltetracarboxylic acid,1,3,5,7-naphthalenetetracarboxylic acid, 2,4,6-pyridinetri-carboxylicacid, 3,5,3′,5′-bipyridyltetracarboxylic acid,3,5,3′,5′-benzophenonetetracarboxylic acid and1,3,6,8-acridinetetracarboxylic acid are most particularly preferred,and even more particularly trimesic acid and1,2,4,5-benzenetetracarboxylic acid.

Mention is also made of multifunctional compounds whose core is aheterocycle containing a point of symmetry, for instance1,3,5-triazines, 1,4-diazines, melamine, compounds derived from2,3,5,6-tetraethylpiperazine, 1,4-piperazines and tetrathiafulvalenes.Mention is made more particularly of1,3,5-triazine-2,4,6-triaminocaproic acid (TTAC).

According to one particularly advantageous embodiment, the copolyamideis obtained from systems of monomers (I), (II) and (III), of which themonomers (II) and (III) are chosen from the following systems:

-   -   system 1: monomer (II) A₃ and monomer (III) B₃    -   system 2: monomer (II) A₄ and monomer (III) B₃    -   system 3: monomer (II) A₃ and monomer. (III) B₄    -   system 4: monomer (II) A₄ and monomer (III) B₄    -   system 5: monomer (II) A₃ and monomer (III) B₆    -   system 6: monomer (II) A₄ and monomer (III) B₆

According to one preferred embodiment, no monofunctional monomer is usedin addition to the monomers (I), (II) or (III).

In order to be able to perform the polymerization under the bestpossible conditions, monomers with a sufficient heat stability are mostparticularly preferred for the monomers (I), (II) and (III).

According to one advantageous characteristic, the melt flow index of thecopolyamides, measured at 275° C. under 5 kg of pressure, is less than10 g/10 minutes.

The invention also relates to compositions comprising the copolyamidedescribed above. The compositions may comprise at least one polyamide inaccordance with the invention and optionally other additives such asmolding or mold-stripping agents, heat-stabilizers, light-stabilizers,antioxidants, flame retardants, pigments, colorants and lubricants. Thecomposition may also comprise agents for improving the impact strengthand/or bulking or reinforcing fillers. Mention is made in particular ofglass fibers.

The compositions of the invention may also comprise as polymer matrix,in addition to the polyamide as described above, other thermoplasticmaterials such as linear aliphatic polyamides, optionallycompatibilized, or aromatic or semiaromatic polyamides, for example.

According to one characteristic of the invention, the compositions ofthe invention are obtained by blending, generally in a single-screw ortwin-screw extruder, a polyamide in accordance with the invention withthe various additives, this blending generally being performed with thepolyamide melt, followed by extrusion of the blend in the form of rodsthat are then chopped into granules. Molded parts may then be made bymelting the granules produced above and feeding the composition meltinto suitable molding, injection-molding or extrusion devices.

A subject of the invention is also a process or manufacturing acopolyamide in accordance with the invention.

In a first embodiment of this manufacturing process, a mixture ofmonomers is prepared with determined proportions of each component. Saidmixture is polymerized under conditions and according to a procedureequivalent to those used for the manufacture of the linear polyamidecorresponding to the difunctional monomers used. Thus, whenε-caprolactam is used, water is added to the mixture of monomers toinitiate the hydrolytic opening of the caprolactam.

According to a second embodiment of the invention, a linear polyamideprepolymer is manufactured by polycondensation of the monomers (I) toobtain a prepolymer with a number-average molecular weight {overscore(Mn)} of the order of 2 000 to 3 000 approximately.

The monomers (II) and (III) are added to the linear prepolymer and thepolymerization is continued either in molten medium or in solid phase.The solid-phase production method makes it possible especially to obtaincopolyamides using multifunctional monomers that show heat stability atrelatively low temperatures, for example below 200° C., since thesolid-phase postcondensation temperature is reached at lowertemperatures than those for polymerization in molten medium.

The addition of the monomers (II) and (III) may be performed in theextruder or in a reactor, the solid-phase postcondensation being carriedout according to the standard conditions usually used for that of linearpolyamides.

The invention also relates to a process for manufacturing novelcopolyamides or novel compositions by extrusion, and to the copolyamidesor compositions obtained by the process. This process usesmultifunctional compounds, under conditions similar to those describedabove, and lead to macromolecular compounds or compositions whosecharacteristics are similar if not identical to those of thecopolyamides and compositions described above.

A process is thus proposed for the manufacture of a copolyamide or acomposition comprising a copolyamide, which consists in mixing in anextrusion device at least the following three compounds:

-   -   compound (I): a polyamide containing repeating units of        formula (c) below:        —[NH—R₁—CO]—  (c)    -   compound (II): monomer (II) as defined above    -   compound (III): monomer (III) as defined above the ratios        $\frac{ax}{{ax} + {by}}$    -    being between 0.4 and 0.6,        -   in which x represents the number of moles of compound (II)            and y represents the number of moles of compound (III)    -   the ratio        $\frac{{ax} + {by}}{\left( {a + b} \right)*\left( {x + y + z} \right)}$    -   being less than 0.3% and preferably 0.2%,        -   in which z represents the number of moles of repeating units            in compound (I)    -   the radical R₁ being a hydrocarbon-based radical optionally        comprising hetero atoms.    -   z is defined in the following manner:        -   z=m_(D)/M_(D) in which m_(D) is the mass of compound (I)            used and M_(D) is the molar mass of a repeating unit.

The ratio $\frac{ax}{{ax} + {by}}$is preferably between 0.45 and 0.55. Even more preferably, it issubstantially equal to 0.5.

The ratio $\chi = \frac{x + y}{x + y + z}$is preferably less than 0.4%.

Compound (I) is preferably chosen from polyamide 6, polyamide 11,polyamide 12 and blends and copolymers based on these polyamides.

The process may comprise the introduction of fillers or additives asmentioned above. Glass fiber is most particularly mentioned.

The copolyamides or compositions according to the invention may be usedin many applications, such as the manufacture of molded orinjection-molded parts.

They are especially suitable for manufacturing parts by extrusionblow-molding techniques. Specifically, the low melt flow index of thecopolyamide makes it possible to limit the deformations of the parisonsduring their extrusion, before the blow-molding step.

It is also possible to manufacture articles by injection-moldingprocesses using the copolyamides of the invention. These articles havemechanical properties that are markedly higher than those of thearticles obtained by injection-molding of a linear polyamide-basedcomposition of the same melt flow index.

Other advantages or details of the invention will emerge more clearly inthe light of the examples given below, purely for indicative purposes.

The following monomers are used:

-   -   CL: mixture of caprolactam and 6-aminocaproic acid (5% by        weight)    -   J3: Jeffamine T 403, sold by the company Huntsman (triamine core        monomer)    -   T4: 2,2,6,6-tetrakis(β-carboxyethyl)cyclohexanone (tetraacid        core monomer).

The copolyamides are synthesized according to the cycle below:

Cycle:

Polymerization in an autoclave for 5 hours at atmospheric pressure, at275° C., with circulation of nitrogen.

The characteristics and properties of the copolyamides evaluated are asfollows:

-   -   melt flow index (MFI): evaluated according to standard ISO 1133        at 275° C. under 5 kg or 375 g of pressure.    -   relative viscosity (RV): evaluated in 96% sulfuric acid        solution, according to standard ISO 307,    -   NH₂ and COOH end groups: evaluated by potentiometric analysis in        a 2.5% by weight solution of TFE (trifluoroethanol) at ambient        temperature. Expressed as meg/kg of polymer,    -   crosslinking: evaluated from the dissolution in TFE

EXAMPLES 1 TO 8

Various copolyamides are synthesized, the characteristics of which aregiven in table I. The nature of the monomers (II) and (III) used, andthe amount in molar percentage (respective ratios${\frac{x}{x + y + {0.9*z}}\quad{and}\quad\frac{y}{x + y + {0.9*z}}}\quad$are specified for each copolyamide. The monomer (I) used is the CLmixture.

Monomer (II) Monomer (III) Example (nature, mol %) (nature, mol %) 1 / /2 T4; 0.5 / 3 / J3; 0.5 4 T4; 0.215 J3; 0.285 5 T4; 0.1075 J3; 0.1475 6T4; 0.0645 J3; 0.0855 7 T4; 0.043 J3; 0.057 8 T4; 0.0215 J3; 0.0285

The characteristics and properties are given table II.

TABLE II Weight for the MFI measurement (g/10 of NH₂ COOH Cross- Examplemin) MFI (g) VR (meq/kg) (meq/kg) linking 1 4 325 3.21 42.4 41.4 No 2 55325 2.05 20 174 No 3 30 325 2.23 114 29.5 No 4 <0.1 5000 3.05 insolubleinsoluble Yes 5 <0.1 5000 3.13 insoluble insoluble Yes 6 0.22 5000 3.6332.8 25.8 No 7 0.8 5000 3.75 28.6 33.2 No 8 4.5 5000 3.86 33.2 24.2 No

EXAMPLE 9

The rheological properties of various polyamides and copolyamides areevaluated, at different shears. A GOETTFRERT WinRHEO V 3.22 capillaryrheometer is used to do this; at a temperature of 250° C., and pressuresof 65 to 1200 bar. These measurements are performed on the followingpolymers, respectively:

-   -   copolyamide according to example 7    -   copolyamide according to example 8    -   polyamide of example 1.

A BRIEF DESCRIPTION OF THE DRAWINGS

The curves representing the melt viscosity (Pa·s) as a function of theshear (s⁻¹) are given in FIG. 1.

It is observed that the difference in rheological behavior between acopolyamide according to the invention and a linear polyamide is morepronounced at low shear than at high shear. This makes thesecopolyamides according to the invention particularly advantageous,especially for extrusion processes. They show good processability in anextruder (high shear) and also a high viscosity at low shear, afterextrusion, for a blow-molding operation.

1. A copolyamide, comprising macromolecular units at least the followingmonomers: (I) at least one difunctional monomer represented by theabbreviation AB (II) at least one multifunctional monomer represented bythe abbreviation A_(a) in which A represents a carboxylic acid function(III) at least one multifunctional monomer represented by the B_(b) inwhich B represents an amine function the functions A and B being capableof reacting with each other to form an amide unit a and b being numbersthat satisfy the following relationships: a≧2 b≧2 a≧3 if b=2 b≧3 if a=2the ratio $\frac{ax}{{ax} + {by}}$  is between 0.4 and 0.6, in which xrepresents the number of moles of monomer (II) and y represents thenumber of moles of monomer (III) the ratio$\frac{{ax} + {by}}{\left( {a + b} \right)*\left( {x + y + {0.9z}} \right)}$ is less than 0.12%, in which z represents the number of moles ofmonomer (I).
 2. The copolyamide as claimed in claim 1, wherein a≧3 andb≧3.
 3. The copolyamide as claimed in claim 1, wherein it comprises nounit derived from a monofunctional monomer.
 4. The copolyamide asclaimed in claim 1 wherein the ratio $x\frac{x + y}{x + y + {0.9*z}}$ isless than 0.2%.
 5. The copolyamide as claimed in claim 1 wherein themonomers (II) and (III) are chosen from the monomers represented byformula (a)

in which C is a covalent bond or an aliphatic hydrocarbon radical thatoptionally comprises hetero atoms, and containing from 1 to 20 carbonatoms, X respectively represents for the monomers (III) and (II) aradical

R₄ is a linear or cyclic, aromatic or aliphatic hydrocarbon radicalcontaining at least two carbon atoms and optionally comprising heteroatoms, m is an integer between 3 and 8, limits included.
 6. Thecopolyamide as claimed in claim 1 wherein the monomer (I) is chosen fromcaprolactam and aminocaproic acid, and mixtures thereof.
 7. Thecopolyamide as claimed in claim 1 wherein the melt flow index, measuredat 275° C. under 5 kg, is less than 10 g/10 minutes.
 8. The copolyamideas claimed in claim 1 wherein it is obtained by mixing, in an extrusiondevice, at least the following three compounds: compound (I): apolyamide containing repeating units of formula (c) below:—(NH—R₁—CO]—(c) compound (II): monomer (II) as defined above compound(III): monomer (III) as defined above the ratio$\frac{ax}{{ax} + {by}},$ being between 0.4 and 0.6, in which xrepresents the number of moles of compound (II) and y represents thenumber of moles of compound (III) the ratio$\frac{{ax} + {by}}{\left( {a + b} \right)*\left( {x + y + z} \right)}$ being less than 0.3% in which z represents the number of moles ofrepeating units in compound (I) the radical R₁ being a hydrocarbonradical optionally comprising hetero atoms.
 9. A composition comprisinga copolyamide matrix and a reinforcing filler, wherein the matrixconsists of a copolyamide as claimed in claim
 1. 10. A yarn, fiber,filament, molded or injection-molded article, or film consisting of acopolyamide or of a composition as claimed in claim
 1. 11. An articleobtained by extrusion blow-molding of a polyamide or of a composition asclaimed in claim
 1. 12. The copolyamide as claimed in claim 5, wherein Cis a aliphatic hydrocarbon radical optionally comprising hetero atoms,and containing from 1 to 6 carbon atoms.
 13. The copolyamide as claimedin claim 8, wherein the ratio$\frac{{ax} + {by}}{\left( {a + b} \right)*\left( {x + y + z} \right)}$is less than 0.2%.